1. Field of the Invention
The present invention relates to a stereo microphone, and more specifically, to a stereo microphone having more simple structure for making an angle formed by the main axes of respective two microphone units variable compared with that of a conventional counterpart.
2. Description of the Related art
An XY stereo system and an MS stereo system are known as a sound pickup system of a stereo microphone. In the XY stereo system, two unidirectional microphone units form an appropriate angle. The microphone unit directed to the left side and the microphone unit directed to the right side output an L channel output and an R channel output, respectively. The microphone units are mechanically fixed at positions in which the main axes thereof form an angle suitable for stereo sound pickup. A technique is known that can make an angle formed by the main axes of the respective microphone units variable (see, for example Japanese Utility Model Application Publication S57-23988).
In the MS stereo system, a unidirectional microphone unit and a bidirectional microphone unit are used. A main signal M obtained from the unidirectional microphone unit and a directional signal S obtained from the bidirectional microphone unit directed to a direction orthogonal to that of the unidirectional microphone unit are fed to a matrix circuit to generate (M+S) and (M−S) signals. For example, the (M+S) signal is an L channel output and the (M−S) signal is an R channel output (see for example, Japanese Patent Application Publication 2002-374592).
The XY stereo system, which can be established with a more simple circuit configuration compared with the MS stereo system, is mainly employed in a low-cost stereo microphone. The stereo microphone disclosed in Japanese Utility Model Application Publication S57-23988 is explained as an example of a conventional stereo microphone employing the XY stereo system. FIG. 3 is an overall view of the stereo microphone disclosed in Japanese Utility Model Application Publication S57-23988. FIG. 4 is an enlarged cross-sectional view of a casing of a microphone unit. In FIG. 3, this stereo microphone 100 includes a microphone casing 102 incorporating the microphone unit and a grip 103 for the user to hold the stereo microphone 100. The microphone casing 102 is provided with a rotary switch 104 at an external portion. The rotary switch 104 mechanically moves the direction of the microphone units incorporated in the microphone casing 102.
The microphone casing 102 incorporates: two microphone units 105 and 106 respectively forming the left and the right channels; microphone supporters 107 and 108 that mechanically support the microphone units 105 and 106, respectively; and a cam 109 that moves the microphone supporters 107 and 108 in accordance with the operation of the rotary switch 104 (see FIG. 3).
The directions of the microphone units 105 and 106 are changed by the movement of the microphone supporter 107 and 108 in accordance with the rotation of the cam 109 made by operating the rotary switch 104 (see FIG. 3). An angle formed by the main axes of the respective microphone units can be set to an angle (for example, 120 degrees) suitable for stereo sound pickup in the above-described manner.
As described with reference to the stereo microphone unit disclosed in Japanese Utility Model Application Publication S57-23988, a structure for mechanically changing and fixing an angle formed by the main axes of the respective microphone units requires many components other than a component for fixing the microphone units, e.g., a component for moving the microphone units or the fixing component, a component for maintaining a resultant angle of the movement by the moving component, and a component for changing the angle. Naturally, combination of such large number of components for making the angle formed by the main axes variable leads to a complex structure.